Rewrite HTTP request and response headers with Azure Application Gateway - Azure PowerShell

This article describes how to use Azure PowerShell to configure an Application Gateway v2 SKU instance to rewrite the HTTP headers in requests and responses.

If you don't have an Azure subscription, create a free account before you begin.

Before you begin

• You need to run Azure PowerShell locally to complete the steps in this article. You also need to have Az module version 1.0.0 or later installed. Run Import-Module Az and then Get-Module Az to determine the version that you have installed. If you need to upgrade, see Install Azure PowerShell module. After you verify the PowerShell version, run Login-AzAccount to create a connection with Azure.
• You need to have an Application Gateway v2 SKU instance. Rewriting headers isn't supported in the v1 SKU. If you don't have the v2 SKU, create an Application Gateway v2 SKU instance before you begin.

Create required objects

To configure HTTP header rewrite, you need to complete these steps.

1. Create the objects that are required for HTTP header rewrite:

   • RequestHeaderConfiguration: Used to specify the request header fields that you intend to rewrite and the new value for the headers.

   • ResponseHeaderConfiguration: Used to specify the response header fields that you intend to rewrite and the new value for the headers.

   • ActionSet: Contains the configurations of the request and response headers specified previously.

   • Condition: An optional configuration. Rewrite conditions evaluate the content of HTTP(S) requests and responses. The rewrite action will occur if the HTTP(S) request or response matches the rewrite condition.

     If you associate more than one condition with an action, the action occurs only when all the conditions are met. In other words, the operation is a logical AND operation.

   • RewriteRule: Contains multiple rewrite action / rewrite condition combinations.

   • RuleSequence: An optional configuration that helps determine the order in which rewrite rules execute. This configuration is helpful when you have multiple rewrite rules in a rewrite set. A rewrite rule that has a lower rule sequence value runs first. If you assign the same rule sequence value to two rewrite rules, the order of execution is non-deterministic.

     If you don't specify the RuleSequence explicitly, a default value of 100 is set.

   • RewriteRuleSet: Contains multiple rewrite rules that will be associated to a request routing rule.

2. Attach the RewriteRuleSet to a routing rule. The rewrite configuration is attached to the source listener via the routing rule. When you use a basic routing rule, the header rewrite configuration is associated with a source listener and is a global header rewrite. When you use a path-based routing rule, the header rewrite configuration is defined on the URL path map. In that case, it applies only to the specific path area of a site.

You can create multiple HTTP header rewrite sets and apply each rewrite set to multiple listeners. But you can apply only one rewrite set to a specific listener.

Sign in to Azure

Connect-AzAccount
Select-AzSubscription -Subscription "<sub name>"

Specify the HTTP header rewrite rule configuration

In this example, we'll modify a redirection URL by rewriting the location header in the HTTP response whenever the location header contains a reference to azurewebsites.net. To do this, we'll add a condition to evaluate whether the location header in the response contains azurewebsites.net. We'll use the pattern (https?)://.*azurewebsites.net(.*)$. And we'll use {http_resp_Location_1}://contoso.com{http_resp_Location_2} as the header value. This value will replace azurewebsites.net with contoso.com in the location header.

$responseHeaderConfiguration = New-AzApplicationGatewayRewriteRuleHeaderConfiguration -HeaderName "Location" -HeaderValue "{http_resp_Location_1}://contoso.com{http_resp_Location_2}"
$actionSet = New-AzApplicationGatewayRewriteRuleActionSet -ResponseHeaderConfiguration $responseHeaderConfiguration
$condition = New-AzApplicationGatewayRewriteRuleCondition -Variable "http_resp_Location" -Pattern "(https?):\/\/.*azurewebsites\.net(.*)$" -IgnoreCase
$rewriteRule = New-AzApplicationGatewayRewriteRule -Name LocationHeader -ActionSet $actionSet -Condition $condition
$rewriteRuleSet = New-AzApplicationGatewayRewriteRuleSet -Name LocationHeaderRewrite -RewriteRule $rewriteRule

Retrieve the configuration of your application gateway

$appgw = Get-AzApplicationGateway -Name "AutoscalingAppGw" -ResourceGroupName "<rg name>"

Retrieve the configuration of your request routing rule

$reqRoutingRule = Get-AzApplicationGatewayRequestRoutingRule -Name rule1 -ApplicationGateway $appgw

Update the application gateway with the configuration for rewriting HTTP headers

In this example, the rewrite set would be associated instantly against a basic routing rule. In case of a path based routing rule, the association would not be enabled by default. The rewrite set can be enabled either via checking the paths on which it needs to be applied via portal or by providing a URL path map config specifying the RewriteRuleSet against each path option.

Add-AzApplicationGatewayRewriteRuleSet -ApplicationGateway $appgw -Name $rewriteRuleSet.Name  -RewriteRule $rewriteRuleSet.RewriteRules
Set-AzApplicationGatewayRequestRoutingRule -ApplicationGateway $appgw -Name $reqRoutingRule.Name -RuleType $reqRoutingRule.RuleType -BackendHttpSettingsId $reqRoutingRule.BackendHttpSettings.Id -HttpListenerId $reqRoutingRule.HttpListener.Id -BackendAddressPoolId $reqRoutingRule.BackendAddressPool.Id -RewriteRuleSetId $rewriteRuleSet.Id
Set-AzApplicationGateway -ApplicationGateway $appgw

Delete a rewrite rule

$appgw = Get-AzApplicationGateway -Name "AutoscalingAppGw" -ResourceGroupName "<rg name>"
Remove-AzApplicationGatewayRewriteRuleSet -Name "LocationHeaderRewrite" -ApplicationGateway $appgw
$requestroutingrule= Get-AzApplicationGatewayRequestRoutingRule -Name "rule1" -ApplicationGateway $appgw
$requestroutingrule.RewriteRuleSet= $null
set-AzApplicationGateway -ApplicationGateway $appgw

Next steps

To learn more about how to set up some common use cases, see common header rewrite scenarios.